This invention relates to the field of environment-remediation systems, and in particular to a system and method for controlling the hydraulic gradient between a contained area and a non-contained area to minimize the potential for flow of aqueous matter through non desirable areas of permeable barriers. Of particular note, the invention addresses the option for treatment of fluids that enter the system during movement between the contained area and non-contained area.
The containment of environmental contaminants in groundwater is an area of ongoing concern. When contaminants are found in environmental media such as soil or groundwater, efforts are often undertaken to prevent an expansion of the contaminated area. In severe contamination cases, containment structures are used to restrict the flow of contaminants and groundwater from the area. These containment structures are typically designed to be keyed into a less permeable geologic formation and placed at the periphery of the contaminated area, and extend from the designed depth to the ground-surface. For ease of reference, the terms “inside-area” and “outside-area” are used hereinafter to distinguish between areas within the containment structure and areas outside the containment structure. Note that, depending upon the particular geology, the containment structure may not necessarily be constructed to form a closed perimeter, relying in part on the natural contour of the land or other factors to prevent the flow of contaminants away-from the contaminated area. In such cases, the “inside-area” is the area in which the contaminants are expected to be contained, by the containment wall or structure or other means.
With such a containment, means must be provided to remove the water that may accumulate in the inside-area, due to either above-ground sources (rain and other precipitation), or at-or-below-ground sources (natural groundwater flow). Generally, this water must be treated before it is released to the outside-area. In a typical embodiment, pumps and filters are used to pump water from the inside-area, through the filters, for release in the outside-area.
FIG. 1 illustrates a water-treatment system that eliminates the need for a pump, as taught by U.S. Pat. No. 6,116,816, “IN SITU REACTIVE GATE FOR GROUNDWATER REMEDIATION”, issued 12 Sep. 2000 to Suthersan et al., and incorporated by reference herein. A barrier wall 170 separates the inside-area 110 to the right of the wall 170 from the outside-area 110′ to the left of the wall 170. A well 140 is dug in the inside-area, and a pipe 145 from this well 140, below the expected water level 148, traverses the barrier wall 170 to the outside-area. Remediation material 150 is provided in the well 170, preferably contained in permeable bags, to facilitate replacement of the material 150. The pipe 145 leads to a discharge zone 185 in the outside-area 110′, which may include another well (not shown). Porous material 130, such as sand, surrounds the well 140 and the discharge zone 185, to facilitate the flow of water from the inside-area 110 to the outside-area 110′. Viewing tubes 160, 180, 190 are provided for monitoring the state of the system. The containment wall 170 is embedded in low-permeability bedrock 120. As groundwater flows 101 toward the containment wall, it accumulates in the well, via the filtration material 150, and flows to the outside-area whenever the water level 148 exceeds the effective water level in the outside-area.
The system of FIG. 1 exhibits a number of disadvantageous features. If the treatment of fluids does not meet the desired end point concentrations, the system does not have a mechanism to stop the flow of fluids from the contained area 110. Although the use of permeable bags for containing the remediation material 150 facilitates replacement of the material 150, it may be difficult to assure a “seal” about the bags to prevent contaminated materials from entering the well 140 and migrating around the bags through preferential pathways. Additionally, many treatment agents cannot be contained by a bag system. Should contaminants or formation materials enter the well 140, or other problems develop in the well 140, it will be difficult to repair the problem, and, in all likelihood, a costly installation of a new well 140 and pipe 145 may be required.
It has been found that a substantial difference in hydraulic pressure between the inside-area and the outside-area is likely to cause some flow of the water between the areas, via the bedrock 120 and other less-than-perfect seals between the inside-area and outside-area. Although Suthersan et al. do not specify the width of the well 140 and pipe 145, the use of the term ‘well’, and references to the lowering of bags of material 150 into the well indicate relatively narrow conduits for the flow of water, generally in the order of a few inches in diameter. Such a system will not necessarily have a significant impact on equalizing the hydraulic pressures between the inside-area and the outside-area, and the likelihood of contaminated water passing from the inside-area to the outside-area in an uncontrolled fashion remains.
It is an object of this invention to provide a mechanism for controlled flow from containment systems such that uncontrolled flow through the containment structure of contaminated liquids is minimized. It is a further object of this invention to provide a flow option for containment systems that is cost-effective to operate and maintain.
These objects, and others, are achieved by providing a system that serves to control the hydraulic gradient between the area within a containment system and the area outside the containment system, coupled with an option of treating contaminated fluids. Preferably, the treatment system includes a large conduit between the inside-area and the outside-area that is accessible via a manhole. This conduit can be filled with materials for the treatment of groundwater, the manhole-sized access providing a relatively easy means of providing and replacing this material. Because the conduit design can easily be scaled up or down in size as appropriate for a given hydrogeologic setting, large hydraulic pressures on either side of the open conduit can be expected to be substantially equal. Gates and screens are provided on either side of the conduit, to facilitate flow control, with manhole accessways to facilitate maintenance of these gates and screens.
Throughout the drawings, the same reference numerals indicate similar or corresponding features or functions. The drawings are included for illustrative purposes and are not intended to limit the scope of the invention.